Optical fibers have acquired an increasingly important role in the field of communications, frequently replacing existing copper wires. This trend has a significant impact in local area networks (i.e., for fiber-to-home uses), which has seen a vast increase in the usage of optical fibers. Further increases in the use of optical fibers in local loop telephone and cable TV service are expected, as local fiber networks are established to deliver ever greater volumes of information in the form of data, audio, and video signals to residential and commercial users. In addition, use of optical fibers in home and commercial business environments for internal data, voice, and video communications is expected to increase.
Optical fibers are often bundled together to form an optical fiber ribbon. The ribbon includes side-by-side and parallel optical fibers that have been encased or encapsulated in a polymeric matrix material. The matrix portion of the optical fiber ribbon can include one or more layers of the polymeric matrix material, and each optical fiber typically contains a dual layer coating system that includes a soft, inner polymer coating and a hard, protective outer polymer coating. Prior to forming the ribbon, the optical fibers may also be coated with a thin colored layer of marking ink (i.e., in a polymer base) for purposes of fiber identification within the ribbon.
While the most basic function of the matrix materials is to secure the individual optical fibers or ribbon sub-units in a planar array, they also contribute to the handling properties of the ribbon. Two important handling attributes of conventional optical fiber ribbons are peel and breakout performance. Peel is the removal of matrix material from the optical fibers in either the mid-span region or the end of the optical fiber ribbon. It is considered desirable, for example, to be able to peel the matrix layers cleanly off the optical fibers without removing any of the colored marking ink layers. In addition, the matrix layers should be removable as an intact unit without breaking apart and leaving residue on the optical fibers. Breakout occurs at the ends of the ribbons and is used to provide access to individual fibers in a ribbon. As with peel, it is desirable to be able to remove all fibers without damage from the matrix material during breakout without it breaking apart and leaving residue on the optical fibers.
Conventional ribbon products have some degree of peel and breakout fiber access. There are various methods, designs and tools available to access fibers, and all require some limited or controlled “bond” between the fibers and the ribbon bonding matrix material. This bond is typically controlled by proper selection and design of the UV ink and matrix materials. The curing of the fiber ink color layer in an inert environment is also a requirement. The goal of the inert environment is to significantly reduce oxygen levels while curing (typically this is less than about 100 parts per million (ppm) oxygen in a nitrogen base environment). Oxygen, if present during curing at levels above about 100 ppm, will react with the free radicals formed for chain propagation and essentially stop the reaction at the outer surface of the ink color layer. In contrast, curing with an oxygen content at less than about 100 ppm provides a controlled bond between the fibers and the ribbon matrix, but ultimately reduces the toughness or durability of the ribbon. For example, when the ribbon is incorporated into a cable and pulled through tortuous paths and/or twisted, portions of the ribbon matrix may separate from the fibers and/or fracture at locations of high stress. “Twist failure” and other forms of ribbon damage may increase attenuation or even cause fibers to go dark.